It is known that inducing turbulence in the active gas makes it possible to obtain uniform and stable discharges in large diameter tubes. H. BRUNET, M. MABRU and . GASTAUS, "Gas flow and Chemical Lasers" 1986, ed. by S. Rosenwaks (Springer Verlag, 1986), p. 40. Discharges in CO.sub.2 -H.sub.2 -He mixtures are characterized by high power densities varying from more than 20 W/cm.sup.3 for small diameter tubes (e.g. 2 cm) to about 2.5 W/cm.sup.3 for tubes of 10 cm diameter.
In such discharges, the electric field extends along the flow direction and along the radiation direction and the discharge is then called a "turbulent axial flow" (TAF) discharge. An experimental industrial CO.sub.2 laser having a power of 7 kW has been made using four tubes having a diameter of 7.5 cm and a length of 80 cm. M. GASTAUD, "Etude de sources laser a gaz carbonique" Rapport EDF. 26 November 1986.
TAF discharges are well adapted to making axial flow lasers. However, they suffer from the drawback of requiring one or two Roots type compressors to be used in order to generate the pressure difference which sets up the turbulence.
CO.sub.2 lasers are also known in which the flow is transverse relative to the radiation direction. These lasers have several advantages which are mentioned below.
In most known transverse flow lasers a uniform discharge is obtained in a volume of several liters by using very many electrodes (several hundred) in order to split up the discharge into as many elementary discharges. (Toshiba) S. IKUTA and S. FUJIWARA, In Technical Digest, CLEO 1985, paper TUC2; (Spectra Physics, Mitsubishi) N. TABATA et al, "Gas Flow and Chemical Lasers" 1984, ed. A. S. Kaye and A. C. Walker (Adam Hilger, 1984) p. 1; (Culham) A. S. KAYE et al, "Gas Flow and Chemical Lasers" 1982, ed. by M. ONORATO (Plenum Press, 1982) p. 383. In general, a single electrode, the cathode or the anode, is segmented with the other electrode remaining single and being constituted by a grid or a bar. For example, in a volume of 20 liters (l) (10 cm.times.10 cm.times.200 cm), the 5 kW Toshiba lasers use a set of 600 cathodes and 3 anodes.
Experiments concerning stabilization by turbulence were described several years ago in addition to using numerous cathodes (one or more per cm). A. C. ECKBRETH and J. W. DAVIS, Appl. Phys. Letters, 19, 101 (1971); W. J. WIEGAND and W. L. NIGHAN, Appl. Phys. Letters, 26, 554 (1975). The turbulence devices were designed to render the speed profile upstream from the cathodes uniform and to set up small scale turbulence.
Other means have also been used for improving the quality of the discharges. In some lasers (Mitsubishi's SAGE laser, Majectic Laser's Pie concept), discharge preionization devices are added in order to increase the uniformity of the discharge.
For small volumes, it is also known to replace D.C. excitation (or A.C. at several kHz) by a radiofrequency discharge (13 MHz or 27 MHz) in order to obtain discharges which are stable and uniform at high pressure. E. HUGEL, Proc. SPIE's 1986, Vol. 650 p. 2; P. HOFFMAN Proc. SPIE's 1986, Vol. 650, p. 23. This technique suffers from the drawback of requiring a radiofrequency power supply which costs more than a D.C. or an A.C. power supply.
The object of the present invention is to increase the amount of electrical power that can be injected into a turbulent transverse flow laser discharge without destabilizing the discharge, thereby, in particular, making it possible to increase the light power of such a laser.
Another object of the invention is to make such a discharge more uniform and/or stable.